This invention relates to an apparatus and process for reducing heat gain and loss through windows and other fenestrations in the heating and cooling of buildings.
Almost half of the energy used in buildings is employed to condition the air. Controlling the temperature, humidity, and quality of the air we breathe is important to our health and comfort. Light is also an important quality to our built environment, and fenestrations provide one or both of those elements. It is through these fenestrations (windows, skylights, and doors) that the majority of energy in a building is gained and lost, usually as heat (as used herein, windows shall include other fenestrations).
In the summer, heat is gained through the glass of a window or the conduction and convection of air passing through an open door. Heat is gained through a window by conduction, radiation, and convection. The ambient air temperature is transmitted through the glass by conduction. Solar radiation is radiated through the glass, and also absorbed and transmitted into the room by convection. In the winter the converse is true; heat is lost through the windows and doors. It is primarily the heat lost and gained through windows due to these exterior temperature influences that can be reduced uniquely with this invention.
Current technology is focused on raising the R value (resistivity) of windows using reflective films, low emissivity coatings, and double and triple glazings that may incorporate chemical dessicants or gases between the panes of glass. Costs are prohibitive for many applications because of specialized technology and complexity.
Window units designed with multiple panes were developed from the study of the effects of draperies on windows. It was noted that draperies played an important role in solar heat control. It was also noticed that when conditioned air was vented over the interior of a window pane, there was an increase in the cooling load to the room. Further study notes the combined effects of venting conditioned air between the window panes and draperies (American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. Handbook).
It is known to vent interior air between the panes of a double pane window assembly to reduce the amount of heat transferred through the assembly.
U.S. Pat. No. 4,382,436 to Hager discloses venting air between two panes in a window.
U.S. Pat. No. 4,577,619 to Howe, Jr. discloses an adjustable shade between two panes and a fan to selectively channel air over the shade and into or out of the building.
U.S. Pat. No. 4,534,335 to Rice discloses a solar heat collector and reflector including a plurality of hollow fins transversely disposed across an open window area and selective direction of the air heated within each fin.
U.S. Pat. No. 4,641,466 to Raninen discloses a double paned window with the interior pane having an electric heating element.
Vented double or multiple paned window assemblies (with or without a shade or collector) are inefficient because solar heat energy is absorbed by more than one element (two panes or one pane and a shade). Thus, absorbed heat must be removed from more than one element. Further, the air is ventilated to the exterior of the building as uncontrolled exhaust; its thermal potential is wasted. Moreover, air between two panes of glass will stagnate and stratify due to buoyancy and thermal variations in the surrounding structure, depending on the location of the air inlet and outlets.
A certain amount of ventilation (currently 5 cubic feet per minute per person) is required under present standards in order to provide adequate ventilation. Recently, concerns about the quality of indoor air have increased interest in ventilation of buildings in order to alleviate "sick building syndrome." However, increased ventilation will increase the load on a building's heating and cooling system because of the increased volume of air that must be conditioned.
It is therefore an object of this invention to provide a simple means to reduce heat gain and loss through windows and other fenestrations.
It is a further object of this invention to provide such a means that utilizes the previously wasted thermal potential of ventilated interior air.
It is a further object to provide such a means that will not unduly increase the volume of air that must be conditioned by a building's heating and cooling systems.
It is a still further object of this invention to provide such a means that can be retro-fitted to existing windows and fenestrations.